Early Harvest by paying its mana cost, untapping at least five basic lands.
Cast a copy of
Regrowth from exile by paying ({1} magic symbol) ({G} magic symbol) , targeting
Early Harvest.
Spellweaver Helix's last ability triggers, allowing you to cast the Extra Combat Sorcery, giving you an additional combat phase and an additional main phase this turn.
Resolve the copy of
Regrowth, returning
Early Harvest from your graveyard to your hand.
Declare
Emeritus of Abundance as an attacker.
When
Emeritus of Abundance attacks, it triggers, becoming prepared.
Repeat each main phase.
Notes
Note that this does not work with cards that care about the "first postcombat main phase" or similar, such as World at War.